Răspuns:
Explicație pas cu pas:
[tex]=\frac{1}{2}+\frac{1}{6}+\frac{1}{12} +...+\frac{1}{110}=\frac{1}{1}-\frac{1}{2}+\frac{1}{2} -\frac{1}{3} +\frac{1}{3} -\frac{1}{4} +...+\frac{1}{10}-\frac{1}{11} =1-\frac{1}{11}=\frac{10}{11}[/tex]
am folosit egalitatea 1/(n·(n+1)) = 1/n - 1/(n+1) .
